Pertussis toxin-sensitive G(i)-proteins and intracellular calcium sensitivity of vasoconstriction in the intact rat tail artery

Abstract

1. We studied the involvement of pertussis toxin (PTX)-sensitive G-proteins in the sensitivity of arterial constriction to intracellular calcium ([Ca2+](i)) mobilization. 2. Vasoconstriction was measured in vitro in perfused, de-endothelialized rat tail arteries loaed with the calcium-sensitive dye, fura-2 and treated or not with PTX (30-1000 ng ml-1). Arteries were stimulated with noradrenaline (NA, 0.1-100 μM) or KCl (15-120 mM). 3. KCl elicited a smaller vasoconstrictor response (E(max)=94±8 mmHg) than NA (E(max)=198±9 mmHg) although [Ca2+](i) mobilization was similar (E(max)=123±8 and 135±7 nM for KCl and NA, respectively). PTX (1000 ng ml-1) had no effect on [Ca2+](i) mobilization but lowered NA- (but not KCl-) induced vasoconstriction (E(max)=118±7 mmHg). 4. G(i)(/o)-proteins were revealed by immunoblotting with anti-G(ix) and anti-G(ox) antibodies in membranes prepared from de-endothelialized tail arteries. [α32P]-ADP-ribosylation of G-proteins by PTX (1000 ng ml-1) was demonstrated in the intact rat tail artery (pixels in the absence of PTX: 3150, presence: 25053). 5. In conclusion, we suggest that smooth muscle cells possess a PTX-sensitive G(i)-protein-mediated intracellular pathway which amplifies [Ca2+](i) sensitivity of contraction in the presence of agonists such as NA.